Injection molding tools and SMC molding tools traditionally have been made of high strength tool steel because of its rigidity and durability. In the automotive industry, molds made of tool steel have been used to injection or compression mold automobile parts made of either thermoplastic or thermoset plastic materials. However, these steel molds are very costly due to the extensive machining required to make them.
It is a common practice in the automotive industry that before a new car is put into production, a limited number of concept or prototype cars are first built for testing. Designing forming tools with tool steel for molding plastic parts used in these prototype cars would not be practical for several reasons. First, a prototype car has to be built in a relatively short time which prohibits the use of tool steel for forming tools due to the extensive machining required. Secondly, the design of a prototype car is changed many times from the original design before it reaches a final production model. This means that many forming tools will have to be built before the design of a specific part is finalized. This makes the building of a steel forming tool prohibitive for cost reasons.
To remedy these problems, castable polymeric materials have been used to make prototype sheet metal stamping tools in recent years. One of these materials is epoxy. For instance, U.S. Pat. No. 4,423,094 to Dearlove et al and assigned to General Motors Corporation discloses a tough, durable epoxy novolac material for use in making sheet metal stamping dies. While this material exhibits good mechanical strength for tooling purposes, it can be used at mold temperatures of up to 150.degree. C. only. This limits its use to sheet metal stamping tools. In most injection molding and SMC molding tools, the tooling material for the mold should remain stable at temperatures higher than 150.degree. C. Another drawback of the Dearlove et al epoxy tooling composition is the high cost of the epoxy novolac resin.
It is therefore an object of the present invention to provide an epoxy tooling composition that can be used in injection molding or SMC molding tools at mold temperatures higher than 150.degree. C.
It is another object of the present invention to provide an epoxy tooling composition that can be used in a cast-to-size injection molding or SMC molding tool at mold temperatures higher than 150.degree. C.
It is yet another object of the present invention to provide an epoxy tooling composition of high compressive strength that can be used in a cast-to-size injection molding or SMC molding tool at mold temperatures higher than 150.degree. C.